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Table 6:

Comparison of the deduced fractional abundances to other observational studies and theoretical predictions.
  12CO 13CO CS HCN CN SiO SiS SO SO2

Lindqvist et al. (1988)a 		$1.5 \times 10^{-4}$ - $1.5 \times 10^{-7}$ $3.0 \times 10^{-7}$ - - $3.5 \times 10^{-7}$ - -
Omont et al. (1993)b - - - - - $1.5 \times 10^{-6}$ - $9 \times 10^{-7}$ $2.05 \times 10^{-6}$
Bujarrabal et al. (1994)c $1.5 \times 10^{-4}$ $1.6 \times 10^{-5}$ $5.0 \times 10^{-8}$ $4.9 \times 10^{-7}$ - $8.5 \times 10^{-6}$ $2.2 \times 10^{-7}$ $1.3 \times 10^{-6}$ -
Kim et al. (2010)d (``case A'') $1.5 \times 10^{-4}$ $1.75 \times 10^{-5}$ $3.0 \times 10^{-7}$ $1.4 \times 10^{-6}$ $1.6 \times 10^{-7}$ $1.3 \times 10^{-5}$ $1.3 \times 10^{-6}$ $7.8 \times 10^{-7}$ $1.4 \times 10^{-5}$
Kim et al. (2010)d (``case B'') $1.5 \times 10^{-4}$ $1.75 \times 10^{-5}$ $8.1 \times 10^{-8}$ $4.3 \times 10^{-7}$ $5.1 \times 10^{-8}$ $5.1 \times 10^{-6}$ $3.1 \times 10^{-7}$ $2.7 \times 10^{-7}$ $4.2 \times 10^{-6}$

González Delgadoe 		                 
et al. (2003) $1.0\times10^{-4}$ - - - -   $2.0 \times 10^{-7}$ - - -
Schöier et al. (2007a)f $1.0\times10^{-4}$ - - - - - $5 \times 10^{-6}$ - -
              - $5.0 \times 10^{-9}$    
this work $1.0\times10^{-4}$ $7.1 \times 10^{-6}$ $4 \times 10^{-8}$ $2.2 \times 10^{-7}$ $1.0 \times 10^{-10}$ $8.0 \times 10^{-6}$ $5.5 \times 10^{-6}$ $2.0 \times 10^{-7}$ $1.0 \times 10^{-6}$
          - $3.0\times 10^{-8}$ - $2.0 \times 10^{-7}$ - $4.0 \times 10^{-9}$    

Duari et al. (1999)h 		$5.38 \times 10^{-4}$ - $2.75 \times 10^{-7}$ $2.12 \times 10^{-6}$ $2.40 \times 10^{-10}$ $3.75 \times 10^{-5}$ $3.82 \times 10^{-10}$ $7.79 \times 10^{-8}$ -
Cherchneff (2006)i $6.71 \times 10^{-4}$ - $1.85 \times 10^{-5}$ $9.06 \times 10^{-5}$ $3 \times 10^{-11}$g $4.80 \times 10^{-5}$ $7 \times 10^{-8}$ $1 \times 10^{-7}$ $1 \times 10^{-12}$
Willacy & Millar (1997)j $4 \times 10^{-4}$ - $2.9 \times 10^{-7}$ $1.4 \times 10^{-7}$ $3.5 \times 10^{-7}$ $3.2 \times 10^{-5}$ $3.5 \times 10^{-6}$ $9.1 \times 10^{-7}$ $2.2 \times 10^{-7}$

Notes. In the first part of the table, observational results are listed based on the assumption of optically thin emission and a population distribution which is thermalized at one excitation temperature. The second part gives observational results based on a non-LTE radiative transfer analysis. Theoretical predictions for either the inner envelope (Cherchneff 2006; Duari et al. 1999) or outer envelope (Willacy & Millar 1997) fractional abundances are given in the last part.
All fractional abundances are given relative to the total H-content. In cases where values found in literature were given relative to H2, they were re-scaled relative to the total H-content by assuming that all hydrogen is in its molecular form H2.

References. (a) No information on used distance and mass-loss rate; (b) distance is 270 pc, $\dot{M}$ = 4.5 $\times $ 10-6 $M_{\odot }$/yr; (c) distance is 270 pc, $\dot{M}$ = 4.5 $\times $ 10-6 $M_{\odot }$/yr; (d) distance is 250 pc, assumed $\dot{M}$ of 4.7 $\times $ 10-6 $M_{\odot }$/yr, LTE is assumed, ``case B'' represents a solution with a larger outer radius than ``case A''; (e) $r_{\rm e}$ in Gaussian distribution for SiO is 2.5 $\times $ 1016 cm, distance is 250 pc and $\dot{M}$ = 3 $\times $ 10-5 $M_{\odot }$/yr; (f) $r_{\rm e}$ in Gaussian distribution for SiS, distance is 260 pc and $\dot{M}$ = 1 $\times $ 10-5 $M_{\odot }$/yr. For 2-component model: $f_{\rm c}$ is 5.5 $\times $ 10-6 and taken constant out to 1.0 $\times $ 1015 cm and the lower abundance Gaussian component has f0 of 5.0 $\times $ 10-9 and $r_{\rm e}$ of 1.6 $\times $ 1016 cm. Using one (Gaussian) component distribution, f0 is 5 $\times $ 10-8 and $r_{\rm e}$ is 1.6 $\times $ 1016 cm; (g) only value at 5 $R_{\star }$ is given; (h) predicted values at 2.2 $R_{\star }$ in the envelope for IK Tau; (i) predicted values at 2 $R_{\star }$ in the envelope for TX Cam; (j) predicted peak fractional abundances in the outer envelope.


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